Environmental control systems are employed within office buildings, manufacturing facilities, or other such locations where the monitoring and control of heating, ventilation, air-conditioning, fluid flow, air quality, lighting, and/or security is desired. In HVAC systems, for example, such control systems can be used to regulate the air temperature within multiple zones of a building or structure using a number of networked electronic thermostat modules. In the control of refrigeration systems, such control systems can be used to regulate a number of compressors or gas coolers for cooling a desired space within a building or structure. In some systems, a building executive controller can be provided to facilitate connectivity and control over multiple such systems via a single portal such as an operator workstation or terminal. Such executive controllers are typically connected to a number of slave modules via a communications bus operating on a suitable platform such as RS-485, allowing digital data to be transmitted back and forth over relatively long distances across the communications lines of the bus.
The ability to monitor analog signals sent across the communications lines of the bus is sometimes useful in diagnosing and repairing communications problems that can occur from an improper installation job and/or from noise or interference from a nearby component. In some circumstances, for example, such noise can be introduced over the communications lines due to the improper shielding of one of the communications cables and/or from the installation of another device located near the executive controller. Such noise may be particularly prevalent in large buildings or facilities where relatively long cables or wires are employed. In some applications, the improper grounding or installation of one of the control modules or actuators may introduce noise across the communications lines resulting in lower bandwidth and, in some cases, data loss.
The resolution of many of these problems typically requires an on-site visit by a technician equipped with an oscilloscope, line monitor, multi-meter, or other field diagnostic tool. Such on-site visits often increases the costs associated with servicing the control system and can delay the resolution of the problem for a period of time, affecting operations within the building or structure.